An organic electroluminescence device including an organic layer which is provided between an anode and a cathode and in which an organic hole transport layer and an organic luminescent layer are laminated attracts attention as a light-emitting device capable of high-luminance emission by low-voltage DC driving. However, the organic electroluminescence device has the problem of low stability with passage of time, such as reduction in luminance and destabilization of emission due to moisture absorption. Therefore, in a display using an organic electroluminescence device, the organic electroluminescence device is covered with a protective film in order to prevent moisture from reaching the organic electroluminescence device.
As such a protective film, an inorganic material film, for example, a silicon nitride film, is used. In order to form this silicon nitride film, it has been proposed to use a plasma CVD method using only SiH4 (silane) gas and N2 (nitrogen) gas as raw material gases without using ammonia (NH3) gas. When such a silicon nitride film formed as described above is used as the protective film, cracking or separation does not occur in the protective film, and the operation of the organic electroluminescence device is also stabilized (refer to Japanese Unexamined Patent Application Publication No. 2000-223264 (particularly, paragraphs 0021-0022)).
Also, there has been proposed a constitution in which in a deposition method using SiH4 (silane) gas, N2 (nitrogen) gas, and H2 (hydrogen) gas as raw material gases, the film density is controlled by changing the nitrogen gas concentration to form a three-layer structure including a high-density silicon nitride film held between low-density silicon nitride films, thereby decreasing residual stress in the protective film and preventing film separation (refer to Japanese Unexamined Patent Application Publication No. 2004-63304 (particularly, paragraphs 0014-0015)).
However, the silicon nitride film formed without using ammonia (NH3) gas as a raw material gas as described above exhibits low transmittance for blue light near a wavelength of 450 nm. Therefore, in a so-called top emission-type display in which light emitted from an organic electroluminescence device is transmitted through the protective film and taken out from the side opposite to a substrate, the emission efficiency of blue light is decreased, thereby decreasing color reproducibility of a full-color display.
On the other hand, when a silicon nitride film formed by the CVD method using ammonia (NH3) gas as a raw material gas is used as the protective film, it is necessary to increase the density of the silicon nitride film by decreasing the deposition rate. However, such a high-density silicon nitride film has low sidewall step coverage and causes a dark spot, thereby causing a defective product. Further, since the deposition rat is low, the manufacturing cost is increased.
Further, when the deposition rate is set to a high value, a decrease in sealing properties of the silicon nitride film causes a reduction in emission lifetime of the device, a reduction in chromaticity, and an increase in driving electric power. In addition, there is a problem in which foreign matter of 50 nm to 300 nm adheres to a surface of the film, thereby failing to maintain quality stability of the protective film.
Accordingly, an object of the present invention is to provide a display in which a light-emitting device can be protected by a protective film having high sealing characteristics and sidewall step coverage and no substance adhering to a surface thereof so that deterioration in the light-emitting device and the occurrence of a dark spot can be prevented, thereby maintaining good display characteristics due to emitted light which is taken out from the protective film side.